In an optical communication system, wavelength-division multiplexing (WDM) is employed for combining several optical carrier signals of different wavelength into a single beam which can then be propagated through a single optical fiber. In practice, channels with close wavelengths may affect one another if they are not sufficiently isolated.
The adjacent channel isolation (AJCI) parameter reflects the remaining power of a dropped channel in the optical fiber. It is one of the key parameters for a wavelength selective switch (WSS) in a reconfigurable optical add/drop multiplex (ROADM) system.
In some instances, it may be desirable to increase the amount of data passed through a communication system by using more channels, or more distinct wavelengths, within a single fiber. However, increasing the number of ports in a WSS usually leads to a drop in the AJCI. By way of example, a WSS with less than 1×9 ports has about 25 dB AJCI and barely meets the requirements.
Accordingly, it is desirable to solve a problem of cleaning or removing remaining power in dropped channels.